1. Field of the Invention
The present invention relates to bipolar transistors and, more particularly, to a SiGe heterojunction bipolar transistor and a method of forming a SiGe heterojunction bipolar transistor.
2. Description of the Related Art
The performance of silicon germanium (SiGe) heterojunction bipolar transistors has increased dramatically in the past decade. For example, the cutoff frequency (fT) of these transistors has increased from approximately 60 GHz to approximately 400 GHz, while the frequency of maximum oscillation (fmax) of these transistors has increased from approximately 100 GHz to approximately 450 GHz.
This dramatic improvement in performance has allowed silicon-based solutions to be used in a number of high-speed applications. Silicon-based solutions are typically preferred over other solutions because silicon-based solutions have a significantly lower cost of raw materials (compared to III-V materials such as GaAs and InP). In addition, silicon-based solutions also bring a substantial reduction in system cost compared to other solutions due to superior levels of integration, versatility, and manufacturability.
Although silicon-based solutions that utilize current-generation SiGe heterojunction bipolar transistors provide substantially better performance than previous generations of devices and are less expensive to manufacture than other solutions, these current-generation transistors typically suffer from limited scalability and process complexity.
Thus, there is a need for a method of forming high-performance SiGe heterojunction bipolar transistors that is more scalable and less complex.